The present invention relates to a remote copy system for remote copying data from a local site to a remote site, and a control method of such a remote copy system.
Calamities, fires or other disasters such as power failure could cause the loss of data stored in a storage apparatus or the suspension of business using such storage apparatus. A storage system using a storage apparatus needs to possess resistance against these calamities and disasters and ongoingly provide services to customers. Thus, a remote copy system for disaster recovery has been realized.
This remote copy system establishes a remote site in an area that will not be affected by the failure that occurs in a local site, and copies data from the local site to the remote site. When a failure occurs in a storage system established in the local site, the storage system at the remote site takes over the tasks of the storage system at the local site, and the remote site thereby continues to provide services to customers.
There are two methods of remote copying; namely, synchronous remote copy and asynchronous remote copy. Synchronous remote copy is a method of notifying a host system I/O completion report to the host system after the writing (remote copy I/O) of data in a secondary volume of a storage system at a remote site is guaranteed. Therefore, from the perspective of the host system, the writing guaranteed in the primary volume at the local site will also be guaranteed in the secondary volume. Thereby, it is possible to prevent transactions from the host system from becoming lost during disasters. Nevertheless, since the host system is required to wait until the remote I/O is completed, the response performance of the host system will deteriorate.
With asynchronous remote copy, since the host system I/O and the remote copy I/O are processed asynchronously, the storage apparatus at the local site is able to send a host system I/O completion report to the host system without having to confirm that the remote I/O (writing) to the secondary volume is guaranteed. Nevertheless, since the writing guaranteed in the primary volume is not guaranteed in the secondary volume, there is a possibility that the transaction may be lost during disasters, but the performance of the host system will not be affected even when the distance between the sites is increased.
Japanese Patent Laid-Open Publication No. 2006-79568 explains an example of this kind of asynchronous remote copy. The remote copy system explained therein is as follows. In a storage [apparatus] at a secondary site, two local replicas are prepared for a volume storing data transferred from a primary site with asynchronous remote copy, and a pair of the respective local replicas constantly prepares replica data guaranteeing the time ordering by alternately stopping based on a time-designated stop command according to the time of the time stamp given to the write data. Then, data is recovered using these replicas when a failure occurs in the primary site.